In this grant proposal, we outline a plan to model human cancer cell invasion in the mouse based on our recent discoveries in zebrafish. We have shown that mutation of the smooth muscle myosin heavy chain (myh11) gene leads to cystic expansion of the posterior intestine in zebrafish meltdown (mlt) mutant larvae. The Mlt (Myh11) protein, which is restricted to smooth muscle cells, non-autonomously activates epithelial expression of human proinvasion gene orthologs in the intestine of zebrafish mlt larvae. Thus, mlt mutants may be used to model human cancer cell invasion. Here, we propose to derive transgenic mice in which the mlt point mutation is engineered into the mouse Myh11 locus. Phenocopy of mlt intestinal defects in a mammalian model system will allow us to address questions concerning epithelial architecture and cancer cell invasion that are not feasible using zebrafish. First, the mlt mice may be used to obtain stromal cell lines for use in microarray experiments and organ culture assays. These experiments may lead to the identification of genes encoding conserved stromal signals that direct human cancer cell invasion. Second, the mlt mutants may be mated to other mouse mutants that model human polyposis syndromes. These double mutants will help determine if alteration of Myh11 promotes invasive transformation of benign intestinal polyps. Third, the mlt knock-in mice may be subjected to chemical mutagenesis protocols known to cause formation of intestinal cancers. These experiments will allow us to test whether the myh11 mutation enhances tumor growth and or metastasis. Thus, derivation of mlt mutant mice will enable experiments that may help define the role of human MYH11 in cancer cell invasion. The work described in this grant proposal will help define the molecular mechanisms of cancer cell invasion and metastasis and may lead to new treatments to prevent cancer progression. [unreadable] [unreadable] [unreadable] [unreadable]